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Bicep spread operator

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The spread operator is used to expand an iterable array or object into individual elements. The spread operator allows you to easily manipulate arrays or objects by spreading their elements or properties into new arrays or objects.

Spread

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The spread operator is used to copy properties from one object to another or to merge arrays and objects in a concise and readable way.

Examples

The following example shows the spread operator used in an object:

var objA = { color: 'white' }
output objB object = { shape: 'circle', ...objA }

Output from the example:

Name Type Value
objB object { shape: 'circle', color: 'white' }

The following example shows the spread operator used in an array:

var arrA = [ 2, 3 ]
output arrB array = [ 1, ...arrA, 4 ]

Output from the example:

Name Type Value
arrB array [ 1, 2, 3, 4 ]

The following example shows spread used multiple times in a single operation:

var arrA = [ 2, 3 ]
output arrC array = [ 1, ...arrA, 4, ...arrA ]

Output from the example:

Name Type Value
arrC array [ 1, 2, 3, 4, 2, 3 ]

The following example shows spread used in a multi-line operation:

var objA = { color: 'white' }
var objB = { shape: 'circle'}
output objCombined object = { 
  ...objA 
  ...objB
}

In this usage, comma isn't used between the two lines. Output from the example:

Name Type Value
objCombined object { color: 'white', shape: 'circle' }

The following example shows how to conditionally add an array element:

@allowed(['white', 'black'])
param color string = 'black'

var colorWhite = { color: 'white' }
var colorBlack = { color: 'black' }

output objB object = ((color == 'white')? { shape: 'circle', ...colorWhite} : { shape: 'circle', ...colorBlack})

Output from the example:

Name Type Value
objB object { shape: 'circle', color: 'black' }

The spread operation can be used to avoid setting an optional property. In the following example, accessTier is set only if the parameter tier isn't an empty string.

param location string = resourceGroup().location
param tier string = 'Hot'

var storageAccountName = uniqueString(resourceGroup().id)
var accessTier = tier != '' ? {accessTier: tier} : {}

resource mystorage 'Microsoft.Storage/storageAccounts@2023-05-01' = {
  name: storageAccountName
  location: location
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
  properties: {
    ...accessTier
  } 
}

The preceding example can also be written as:

param location string = resourceGroup().location
param tier string = 'Hot'

var storageAccountName = uniqueString(resourceGroup().id)

resource mystorage 'Microsoft.Storage/storageAccounts@2023-05-01' = {
  name: storageAccountName
  location: location
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
  properties: {
    ...(tier != '' ? {accessTier: tier} : {})
  } 
}

The spread operator can be used to override existing properties.

param location string = resourceGroup().location
param storageProperties {
  accessTier: string?
}

resource mystorage 'Microsoft.Storage/storageAccounts@2023-05-01' = {
  name: uniqueString(resourceGroup().id)
  location: location
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
  properties: {
    accessTier: 'Cold'
    ...storageProperties
  }
}

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